But Holger is himself an excellent PhD economist (he was a classmate of mine)

The cost of international treaties and conventions is curbed national discretion. The benefits are co-operation, often in fields completely separate to the agreement at hand. Only arguing about the costs of the ECHR is like divorcing your wife for not doing the washing up.

Rejoining the EU?

Oh I agree with your main point. I just don't think it's impossible to raise potential output with the right policy mix